This invention relates to a fluid pump with a rotary impeller. More particularly this invention relates to a fluid pump with a bearing-free, seal-free electromagnetically-driven rotary impeller. The impeller is levitated by a combination of axial and radial localized opposed magnetic and fluid forces or by axial and radial magnetic forces only. The magnetic forces used for levitation are generated by a combination of solenoids or diamagnets and permanent magnets, electromagnets or solenoids.
Levitation of the impeller by such forces allows for high efficiency in converting power into useful work. Thus, a relatively small energy source can be used and the life of the energy source is correspondingly extended. Moreover, use of a levitated impeller driven by electromagnetic forces eliminates the need for driving mechanism bearings and seals, thereby avoiding the heat build-up and leakage attendant with other rotary pump inventions. Such considerations can be of critical importance for pumping of physiological fluids such as blood.
A large number of mechanisms for pumping fluids have been described in the art, including, for example, peristaltic pumps, moving diaphragm pumps, piston-type pumps, and centrifugal or rotary pumps. Generally, a rotary pump includes a pumping chamber with inlet and outlet ports and an impeller mounted within the pumping chamber for rotation about an axis. Frequently the impeller is mounted on a shaft that extends through one or more seals and a bearing apparatus to a rotational driving mechanism outside the pumping chamber. Rotary pumps employing shaft-mounted impellers with shaft seals are exemplified in the following U.S. patents: Dorman et al. U.S. Pat. No. 3,608,088; Rafferty et al. U.S. Pat. No. 3,647,324; Reich et al. U.S. Pat. No. 4,135,253; Clausen et al. U.S. Pat. No. 4,589,822; Moise U.S. Pat. No. 4,704,121; and Kletschka U.S. Pat. No. 4,844,707. Shaft seals are susceptible to wear and heat build-up, which can lead to leakage and, in the case of blood pumps, to thrombogenic (clot-forming) problems, denaturation of proteins, and embolic phenomena and the like.
Other pump inventions employ liquid or hydrostatic bearings to reduce heat build-up and/or to dissipate heat and to reduce frictional forces in rotation of the shaft and/or impeller. In these inventions liquid or gas is forced into narrow clearances between the shaft and various bearing assemblies or between the impeller and the impeller housing. The relatively thin fluid or gas films generated in these inventions are nevertheless subject to high shear forces and some incremental heat build-up. The following U.S. patents exemplify the use of such liquid or hydrostatic bearings: Prindle U.S. Pat. Nos. 845,816 and 888,654; Anderson U.S. Pat. No. 2,864,552; Baker et al. U.S. Pat. No. 3,122,101; and Kambe et al. U.S. Pat. No. 4,475,866.
Olsen et al. U.S. Pat. No. 4,688,998 discloses a fluid pump with an electromagnetically driven and levitated impeller. In Olsen et al., a sensor and a controller are provided to sense and control the amount of electromagnetic levitating force applied to the impeller. Only electromagnetic levitating forces are applied to the impeller. Unlike the present invention, in Olsen et al. the levitational forces are provided by electromagnets. In addition, in Olsen et al. the levitational forces are not applied to the impeller in separate and distinct axial and radial directions.
In the fluid pump disclosed in U.S. Pat. No. 5,055,005, which is the grand parent of this application, while all the input energy is directed to rotation of the impeller, a portion of the output energy from the peripheral region of the impeller (which includes locations downstream from the periphery of the impeller) is diverted for use in levitating the impeller by fluid force. Thus, not all of the input energy is directed toward pumping fluid from the pump. The fluid pump disclosed in U.S. Pat. No. 5,195,877, which is the parent of this application is an improvement on the aforementioned fluid pump. In the fluid pump disclosed in U.S. Pat. No. 5,195,877, the impeller is levitated and positioned in the fluid pump by auto-adjusting, permanent repulsive magnetic forces. This makes it possible for more input energy to be directed to rotation of the impeller and pumping of the fluid. The embodiment disclosed herein improves on the fluid pump disclosed in U.S. Pat. No. 5,195,877 and employs a combination of permanent magnets, solenoids, electromagnets or diamagnets to levitate and position the impeller in the fluid pump.